In a ring laser gyroscope (RLG), laser light beams counter-propagate about a closed path. Typically, a path length control loop adjusts the optical path length in the RLG block to maximize the laser output power output from the ring laser gyroscope. When the RLG is at rest in inertial space, the two beams oscillate at the same or substantially the same frequency. If the system rotates in inertial space, the counter-propagating optical laser beams oscillate at different frequencies. The frequency difference is an indication of the rate of rotation.
For small rotation rates of the RLG, optical power backscattering from the laser mirrors causes the counter-propagating optical laser beams to resonate together and “lock-in”. Lock-in degrades the accuracy of a RLG. During lock-in, the RLG is unable to sense rotation. To minimize the lock-in effect, the RLG is dithered (periodically rotated) so that the RLG is in constant motion, rotating periodically, through a zero input rate. Thus, dithering minimizes the time that lock-in can occur. As the dither rotation slows down and approaches the dither turn-around points, the laser beams interact, due to of the RLG block 411 causes an expansion of the RLG block 411.ns of each single beam.
RLGs with large amounts of back scatter exhibit high angular random walk (ARW) and poor gyroscope performance.